Dysfunction of the vascular endothelium contributes to most cardiovascular diseases. This is not surprising, as the endothelium is the central regulator of hemostasis, vascular development, angiogenesis, vasomotor tone, and the response to vascular injury and inflammation. We have used several complimentary approaches during the past funding cycle--taking advantage of previous work from our lab and others indicating an early role for the vascular endothelial growth factor receptor VEGFR-2 in blood vessel growth-- to fill in the gaps in our understanding of how endothelial cell destiny and phenotypic diversity are determined. We have recently defined essential roles for members of the homeobox and bone morphogenetic protein (BMP) families as critical regulators of endothelial cell differentiation and phenotypic modulation. In particular, we have identified the homeodomain protein HoxB5 as the first transcription factor yet described to be sufficient to elicit differentiation of endothelial cells from mesoderm-derived precursors. We have also characterized BMPER, a novel BMP-binding protein, as an angioblast-specific regulator of endothelial growth and differentiation. The present proposal exploits well-characterized aspects of molecular biology, genomics, and cell biology as tools to explore further the earliest steps in blood vessels formation. These tools will allow us to determine how HoxB5 commits precursor cells to assume an endothelial phenotype in AIM #1. The consequences of HoxB5-dependent gene regulation on angiogenesis and endothelial progenitor function will be dissected in AIM #2. In Aim #3, we will delineate the role of BMP family members in regulation of vascular developmental and we will specifically test the role of BMPER in endothelial precursor commitment decisions. Our studies are informed by the general hypothesis that developmental and physiologic vascular processes share fundamental similarities at the molecular level. The scope of the this proposal is intended to address relevant biological and physiological questions using state-of-the-art molecular biology techniques. Knowledge gained from this proposal should provide crucial information about endothelial cell development from multipotent precursors, blood vessel formation in health and disease, and endothelial cell-type specific gene expression. In addition, mechanisms for targeted gene delivery to endothelial cells and for disruption of angiogenesis in its pathologic forms may be revealed. [unreadable] [unreadable] [unreadable]